The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.
When testing a device under test (DUT), such as semiconductor wafers having non-singulated devices thereon, for example, one or more probe cards having an array or pattern of probes that match or mirror the die pads (for example) of the DUT, may be positioned between: (1) the DUT; and (2) a tester to achieve electrical connection there between. In the case of a probe card having cantilever probes, for example, the lower surface of an elongated beam may be bonded to a post at one end of the beam and a probe tip is formed on the upper surface on the other end of the beam to cantilever the beam/probe. The probe tips are designed to make physical and electrical contact with the DUT die pads/contacts.
The planarity and/or co-planarity of the probes and/or probe tips on the probe cards is important to ensure electrical contact of the probe tips to all of the corresponding DUT die pads to be tested, preferably simultaneously, to not only minimize or eliminate false negatives during testing, but to prolong the life of the probes and probe cards. For example, if one or more probe tips extend too far above the probe surface (too-high in the Z-direction, for example), then the probe card may be positioned to ensure contact with the remainder of the probe tips, eventually overstressing these too-high probe tips probes that may lead to premature malfunctioning, damage or even breakage of the probes.
If one or more of the probes/probe tips on the probe cards extends too near the supporting substrate surface (too low in the Z-direction) then the probe array may be positioned (e.g., during testing) to ensure contact with the, presumably minority, too-low probe tips, eventually overstressing the correctly vertically aligned probes that may lead to premature malfunctioning, damage or even breakage of the correctly vertically aligned probes. Further, in the case that some probes/probe tips are too-low and some probes/probe tips are too-high, even greater stress is exerted upon the too-high probes as the probe card is positioned even closer to the DUT to ensure contact between the too-low probe tips and the DUT contacts.
It is also important to ensure that the probes are also horizontally aligned (in the X- or Y-direction, as appropriate), that is, the probes/probe tips are either maintained in substantial parallel alignment with select adjacent probe(s)/groups of probes or at a specified horizontal distance in relation to other probes on the probe cards to ensure contact with the corresponding DUT contacts.
In the normal course of repeated testing of the DUTs many thousands of touchdowns (separate physical contact between the probe tips and the die pads, for example, of the DUTs) may be achieved. This may lead to normal wear and tear on the probes and/or probe tips causing damage or breakage of the probes and/or probe tips and (further) misalignment, either vertically or horizontally, of some or many of the probes and/or probe tips.